Техническое чтение для энергетиков. Бухарова Г.П. - 30 стр.

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when we switch on our electric lamp.
If the circuit is broken or, as we generally say "opened" anywhere, the current is
known to stop everywhere. Hence, we break the circuit when we switch off our
electrical devices. Generally speaking, the current may pass through solid conductors,
liquids, gases, vacuum, or any combination of these. It may flow in turn over
transmission lines from the power-stations through transformers, cables and switches,
through lamps, heaters, motors and so on.
There are various kinds of electric circuits such as: open circuits, closed circuits,
series circuits, parallel circuits and short circuits.
To understand the difference between the following circuit connections is not
difficult at all. When electrical devices are connected so that the current flows from
one device to another, they are said to be connected in series. Under such conditions
the current flow is the same in all parts of the circuit, as there is only a single path
along which it may flow. The electrical bell circuit is considered to be a typical
example of a series circuit. The parallel circuit provides two or more paths for the
passage of current. The circuit is divided in such a way that part of the current flows
through one path, and part through another. The lamps in your room and your house
are generally connected in parallel.
Now we shall turn our attention to the short circuit sometimes called "the short".
The short circuit is produced when the current is allowed to return to the source of
supply without control and without doing the work that we want it to do. The short
circuit often results from cable fault or wire fault. Under certain conditions, the short
may cause fire because the current flows where it was not supposed to flow. If the
current flow is too great a fuse is to be used as a safety device to stop the current
flow.
The fuse must be placed in every circuit where there is a danger of overloading
the line. Then all the current to be sent will pass through the fuse.
When a short circuit or an overload causes more current to flow than the
carrying capacity of the wire, the wire becomes hot and sets fire to the insulation. If
the flow of current is greater than the carrying capacity of the fuse, the fuse melts and
opens the circuit.
A simple electric circuit is illustrated in Fig. 3. In (his figure a 4-cell battery has
been used, the switch being in an open position. If the switch is in a closed position,
the current will flow around the circuit in the direction shown by the arrows.
TERMS AND DEFINITIONS
In the following paragraphs the terms commonly used to distinguish between the
various properties, or ways measuring the properties of alternating current are
described.
Cycle and Period.– The complete series of changes consisting of the growth and
decay of the voltage or current in one direction, together with its growth and decay in
the reverse direction, is called one cycle. A voltage or current that is reproduced at

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